The present invention relates to a process for preparing moisture-curable urethanes containing reactive silane groups from polyether polyols having a low degree of unsaturation and to the use of these polyurethanes as sealants, adhesives and coatings.
Polyether urethanes containing reactive silane groups, also referred to as silane-terminated polyurethanes (STPs), and their use as sealants and adhesives are known and described, e.g., in U.S. Pat. Nos. 5,554,709; 4,857,623; 5,227,434 and 6,197,912; and WO 02/06367. The silane-terminated polyurethanes may be prepared by various methods. In one method the silane-terminated polyurethanes are prepared by reacting diisocyanates with polyether polyols to form isocyanate-terminated prepolymers, which are then reacted with aminosilanes to form the silane-terminated polyurethanes. The sealants may also be prepared by reacting unsaturated monools with diisocyanates to form intermediates containing unsaturated end groups and then converting these unsaturated groups to alkoxysilane groups by hydrosilylation. In another method the sealants are prepared in one step by the reaction of polyether diols with isocyanatosilanes
To be useful as sealants the sitane-terminated polyurethanes should have a number average molecular weight of 6000 to 20,000. One method of obtaining this molecular weight is to use polyether diols prepared by the KOH process and having a molecular weight of 2000 to prepare the isocyanate-terminated prepolymers. The presence of urethane groups causes the products to have a high viscosity. To achieve suitable application viscosities, the high viscosity is reduced by the addition of higher amounts of plasticizer and lesser amounts of fillers, resulting in more expensive sealant products.
Another method of obtaining high molecular weight sealants is by using high molecular weight polyether diols having a low degree of unsaturation and prepared using special catalysts as described in EP-A 0,546,310, EP-A 0,372,561 and DE-A 19,908,562. When these polyether diols are used, the resulting sealants have excellent tensile strength, but the sealants are too brittle for many applications because the elongation is too low and the 100% modulus is too high.
The preparation of sealants from mixtures of polyfunctional and monofunctional silane-terminated polyurethanes is known and disclosed in U.S. Pat. Nos. 5,554,709 and 4,857,623 and WO 02/06367. However, these references do not disclose the use of polyether polyols having a low degree of unsaturation and aspartate-functional silanes to prepare the sealants.
The preparation of silane-terminated polyether urethanes from aspartate-functional silanes is disclosed in U.S. Pat. No. 5,364,955 and WO 98/18843. In both of these references the polyethers used to prepare polyether urethanes do not have a low degree of unsaturation. In addition, mixtures of polyfunctional and monofunctional silane-terminated polyurethanes are not disclosed. Finally, in the latter reference the polyethers must contain 15 to 40% by weight of ethylene oxide units.
WO 00/26271 discloses the preparation of silane-terminated polyether urethanes from polyether polyols having a low degree of unsaturation and aspartate-functional silanes. The products are prepared by reacting diisocyanates with high molecular weight polyether diols to form NCO prepolymers, which are then capped with aspartate-functional silanes to form silane-terminated polyether urethanes. This application does not disclose mixtures of disilane-terminated polyether urethanes with polyether urethanes containing one reactive silane group.
U.S. Pat. No. 6,265,517 describes a similar process for preparing silane-terminated polyether urethanes from polyether polyols having a low degree of unsaturation and aspartate-functional silanes. The patent requires the starting polyol to have a monool content of less than 31 mole %, and teaches that a relatively high monool content is highly undesirable because monools react with isocyanates thereby reducing crosslinking and curing of the prepolymer. The patent also requires the aspartate silanes to be prepared from dialkyl maleates in which the alkyl groups each contain more than four carbon atoms.
EP 0,372,561 discloses polyether urethanes containing reactive silane groups and prepared from polyether polyols having a low degree of unsaturation. In addition, polyether urethanes containing one reactive silane group are disclosed. This application fails to disclose the use of aspartate-functional silanes to incorporate the reactive silane groups.
The deficiencies of the preceding sealants was overcome in copending applications, Ser. Nos. 10/160,479, 10/174,039, 10/173,919, and 10/160,364, which describe moisture-curable, alkoxysilane-functional polyether urethanes containing both polyether urethanes having two or more reactive silane groups and polyether urethanes having one reactive silane group. The moisture-curable polyether urethanes are suitable for use as sealants, adhesives and coatings which possess high tensile strengths and elongations and have a reduced 100% modulus when compared with existing products
In the copending applications the polyether urethane component containing two or more reactive silane groups are prepared from high molecular weight polyether polyols having a low degree of unsaturation. In addition, at least a portion of the reactive silane groups present in at least one of the two components are incorporated by the use of silanes containing secondary amino groups. Finally, the polyether urethane components described in the copending applications are prepared separately and subsequently blended to form the moisture-curable polyether urethanes according to the invention.
One of the disadvantages of these moisture-curable polyether urethanes is that even though the blended product has a low viscosity, the polyether urethane component containing two or more reactive silane groups has a high viscosity and is more difficult to prepare than a lower viscosity product.
Accordingly, it is an object of the present invention to provide moisture-curable polyether urethanes that can be prepared at lower production viscosities and still retain all of the valuable properties of the polyether urethanes disclosed in the copending applications, i.e., the products are suitable for use as sealants, adhesives and coatings which possess high tensile strengths and elongations and have a reduced 100% modulus.
This object may be achieved with process of the present invention in which the moisture-curable polyether urethanes containing a mixture of polyether urethane component having two or more reactive silane groups and a polyether urethane component having one reactive silane group are prepared simultaneously instead of being prepared separately and mixed.
It is surprising that the polyether urethanes obtained according to the process of present invention possess the same properties as the products obtained in accordance with the copending applications because a greater variety of by-products are obtained according to the present invention and it could not be predicted that the presence of these by-products would not affect the valuable properties of the moisture-curable polyurethanes.
The present invention relates to a process for preparing a moisture-curable, alkoxysilane-functional polyether urethane by reacting at an NCO:OH equivalent ratio of 1.5:1 to 2.5:1
a) a hydroxyl component containing
i) 20 to 100% by weight, based on the weight of component a), of a polyether containing two hydroxyl groups and one or more polyether segments, wherein the polyether segments have a number average molecular weight of at least 3000 and a degree of unsaturation of less than 0.04 milliequivalents/g, provided that the sum of the number average molecular weights of all of the polyether segments per molecule averages 6000 to 20,000, and
ii) 0 to 80% by weight, based on the weight of component a), of a polyether containing one hydroxyl group and one or more polyether segments having a number average molecular weight of 1000 to 15,000, with
b) an isocyanate component containing
i) 20 to 100% by weight, based on the weight of component b), of a compound containing two isocyanate groups, and
ii) 0 to 80% by weight, based on the weight of component b), of a compound containing one isocyanate group,
to form an isocyanate-containing reaction product and subsequently reacting this reaction product at an equivalent ratio of isocyanate groups to isocyanate-reactive groups of 0.8:1 to 1.1:1 with
c) a compound containing an isocyanate-reactive group and one more reactive silane groups in which at least 10 mole % of component c) is a compound corresponding to the formula 
xe2x80x83wherein
X represents identical or different organic groups which are inert to isocyanate groups below 100xc2x0 C., provided that at least two of these groups are alkoxy or acyloxy groups,
Y represents a linear or branched alkylene group containing 1 to 8 carbon atoms and
R1 represents an organic group which is inert to isocyanate groups at a temperature of 100xc2x0 C. or a group corresponding to formula II
xe2x80x94Yxe2x80x94Sixe2x80x94(X)3xe2x80x83xe2x80x83(II)
to form a moisture-curable, alkoxysilane-functional polyether urethane, provided that total percentages of a-ii) and b-ii) add up to at least 10.